A touch screen display is a device that can detect an object in contact with or in proximity to a display area. The display area can be covered with a touch-sensitive matrix that can detect a user's touch by way of a finger or stylus, for example. Touch screen displays are used in various applications such as mobile phones, tablets, smartwatches, and other mobile devices. A touch screen display may enable various types of user input, such as touch selection of items on the screen or alphanumeric input via a displayed virtual keypad. Touch screen displays can measure various parameters of the user's touch, such as the location, duration, etc.
One type of touch screen display is a capacitive touch screen display. A capacitive touch screen display may include a capacitive touch matrix of conductive rows and conductive columns overlaid on the display area. The rows and columns are spaced apart from one another so as to not make contact. The capacitive touch screen display may be used for mutual capacitance sensing.
In mutual capacitance sensing, the capacitance between each row and column of the capacitive touch matrix may be sensed. A change in the sensed capacitance between a row and a column may indicate that an object, such as a finger, is touching the screen or is in proximity to the screen near the region of intersection of the row and column. Mutual capacitance sensing circuits employ a “forcing” signal applied to a column of the capacitive touch matrix and sensing of the coupled signal on respective rows (or vice-versa).
When a touch screen controller that provides the forcing signal and that senses the ensuing coupled signal is coupled to the columns and rows, there is a certain inherent capacitance between respective column and row pairs of the touch screen display. Determination of these capacitances is useful for verifying quality of capacitive touch screen displays as they are manufactured. Currently, such determination is performed using external test equipment. However, this can be burdensome and time consuming. Therefore, further advances in determination of these capacitances are desirable.